rtlwifi: rtl8821ae: Make sure loop counter is signed on all architectures

The for-loop condition does not work correctly on architectures where
"char" is unsigned. Fix it by using an "int", which may also result in
more efficient code.
Signed-off-by: David Müller <d.mueller@elsoft.ch>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c

@@ -959,7 +959,7 @@ static void _rtl8821ae_phy_store_txpower_by_rate_base(struct ieee80211_hw *hw)
 static void _phy_convert_txpower_dbm_to_relative_value(u32 *data, u8 start,
 						u8 end, u8 base_val)
 {
-	char i = 0;
+	int i;
 	u8 temp_value = 0;
 	u32 temp_data = 0;